This entry is characterized by proteins with alternating conserved and low-complexity regions. Bud13 together with Snu17p and a newly identified factor, Pml1p/Ylr016c, form a novel trimeric complex. called The RES complex, pre-mRNA retention and splicing complex. Subunits of this complex are not essential for viability of yeasts but they are required for efficient splicing in vitro and in vivo. Furthermore, inactivation of this complex causes pre-mRNA leakage from the nucleus. Bud13 contains a unique, phylogenetically conserved C-terminal region of unknown function.